Change beforeinstallprompt event to take an array of platforms.

Source/modules/app_banner/AppBannerController.h

Index: Source/modules/app_banner/AppBannerController.h
diff --git a/Source/modules/app_banner/AppBannerController.h b/Source/modules/app_banner/AppBannerController.h
index a4f0829325ccf783570537ef1428cdd92a302f4a..fb61727d3ff740c8c6630fe30ae6ab950fa4a7d0 100644
--- a/Source/modules/app_banner/AppBannerController.h
+++ b/Source/modules/app_banner/AppBannerController.h
@@ -10,12 +10,13 @@ namespace blink {
 enum class WebAppBannerPromptReply;
 class LocalFrame;
 class WebString;
+template <typename T> class WebVector;
 
 // FIXME: unless userChoice ends up implemented, this class should not exist and
 // a regular static method could be used instead.
 class AppBannerController final {
 public:
-    static void willShowInstallBannerPrompt(LocalFrame*, const WebString& platform, WebAppBannerPromptReply*);
+    static void willShowInstallBannerPrompt(LocalFrame*, const WebVector<WebString>& platforms, WebAppBannerPromptReply*);
 
 private:
     AppBannerController() = delete;